Introducing enzyme selectivity: a quantitative parameter to describe enzymatic protein hydrolysis.

Enzyme selectivity is introduced as a quantitative parameter to describe the rate at which individual cleavage sites in a protein substrate are hydrolyzed relative to other cleavage sites. Whey protein isolate was hydrolyzed by Bacillus licheniformis protease, which is highly specific for Glu and Asp residues. The molar concentration of all peptides (58) from β-lactoglobulin formed during hydrolysis was determined from the UV214 signal. The quality of identification and quantification of the peptides were described by newly defined parameters: the peptide sequence coverage (on average 94 %) and the molar sequence coverage (on average 75 %). The selectivity was calculated from the rate of hydrolysis of each cleavage site, and showed differences of up to a factor of 5,000. The ability to quantitatively discriminate the enzyme preference towards individual cleavage sites is considered essential to the understanding of enzymatic protein hydrolysis.